Superheterodyne radio system



Feb. 19, 1929.

G. L. BEERS surmammonmn RADIO SYSTEM F iled Feb. 18, 1925 Ear 1 1 1TINVENTOR Geagml. Beer:

ATTORNEY %TNESSES: M

Patented" at. 19, 1929.

GEORGE L. BEERS, or WILKINSBURG, 'rENNsvLvAiiIA, 'ASSIGNOB roWESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATIQN'OFPENNSYLVANIA.-

sUPEmTEnoDYnE RADIO. SYSTEM.

Application nled'l'ebruary s, 1925. Serial No. 10,004.

My invention relates to radio receiving-apparatus and particularly tosuch apparatus as employs the superheterodyne principle;

An object of my invention, is to providea radio receiving apparatus ofhigh selectivit with respect to two frequencies and in whic means areembodied for removingone of the received frequencies. Another object ofparatus embodying means for preventing response to a second frequencywhich may be heterodyned to the beat frequency.

Another object of my invention is to construct a radio-frequencyheterodyne radio receiving apparatus having a drain coil thereln.

I Another object. of my invention is to construct a superheterodyneradio receiving system having means for suppressing a second frequencyto which the system is responsive.

Another object of my invention is to 0.011- struct a superheterodyneradio receiving system having a singletuning hump.

In the'operation of radio receiving a paratus of the superheterodynetype, it has een found that there are two frequencies which may besimultaneously heterdodyned to give the'same beat frequency. Theradio-receptor system may be tuned to a given frequency and "the localoscillator may be adjusted tothe proper frequency to give a beat withthe desired signal of a frequency to whichthe associated amplifierapparatus is responsive. Un-

der theseconditions, the system is sensitive and is responsive to'-verweak signal-energy of the frequency to w ich the receptor is tuned. Therejector properties of the beat frequency amplifiers cause other faintsignals" to "be attenuated to such'an extent that they are notperceptible in connected signal translating apparatus. This attenuationis very marked because the radio receptor is tuned .to a singlefrequency. Therefore, the system is very sensitive and very selective.

As is well known in the art, the superheterodyne radio receiving system.produces at the receiving station a radio-frequency differing fromtheincoming signal frequency and which is-determined by the frequency towhich the amplifier apparatus is tuned. The

local oscillator may be set to generate at a frequency either higher orlower by the desired amount than the incoming signals.

If, in the desired application, the. oscillator my invention is to pro-"duce a superheterodyne radio 'recelvmg apis tuned to a frequency whichis lowcrthan the same amount to react with the oscillationgeneratorfrequency to produce the {same beat frequency as the higher freo'ueney=sig5 nals. Under these conditions, the lowerfre i f quency signalswill be received through tl beat frequency amplifier apparatus. 1f highpower sending apparatus is. in. op-

eration near the receiving appa-ratu's,{ it may force oscillations oflow amplitude in the; 7

radio receptor. If these oscillations differ from the frequency of thelocal oscillator by the same amount that the desired faintsigrials-differ, they will be heterody'nedwto the same frequency, whichfrequency is received and amplified by the associated apparatus and madeaudible by the signal translator.

Such interference is very ob'ectionable, and is deceptive because of theact that it-disappears upon the change in the local oscillator frequencyand may cause the operator to mistakenly believe that he has receivedsignals from the station which he desires to hear.

My. invention provides means whereby such interfering signals at adifferent fre quency than the frequencyto which the 're-" ceptor istuned, and which may be the second 'heterodynefre'quency, are drainedout of the system, or by-passed, before they reach the heterodyneoscillator and thereby are prevented from influencing the balance of thesystem.

Other objectsand structural details of my invention will be apparentfrom the following description when read in connection with theaccompanying drawings, wherein Figure 1 is a diagrammatic. representionof circuits and apparatus embodying a preferred form of my invention;and

Fig. 2'is a diagrammatic representation of circuits and apparatusembodying my invention in a manner in which it is twice applied.

In-the'drawings, a radio-receptor 1,, which may be a loop-antenna, istuned by a condenser 2 and connected to a triode 3 which amplifiesreceived signals at the received frequency. This amplifier for signalsat the incoming frequency is a desirable portion of the invention, butis not an essential part thereof. The amplified output of the repeatertriode 3 is transferred by electromagnetic induction through transformercoils 4 and 5. An oscillation generator 6, of any desired form,

PATENT oFF1cE.-,-

has a tuned circuit 7 which is positioned in 5. Energy incrementstransferred to the coil 5 from the coils 7 and 4 combine to give beatphenomena which are resolved by the triode 8 and its associated circuitinto a beat-note, corresponding with, and proportional to, the energy ofthe original incoming signal. This beat-note, which is modulated inaccordance with the original signal, is amplified by an amplifier 9,detected by a detector 11 and translatedinto sound by a telephonereceiver 12.

A tuned resonant circuit, consisting of an inductor 1 1 and a condenser15, is connected across the terminals of the receptor 1 in parallel withthe tuning condenser 2. The condenser 15 is adjustable and the inductorand condenser together constitute a series resonant circuit having avery low impedance to the frequency to which it is tuned and a very highimpedance to all other frequencies.

The system then operates in the following manner. Signals are receivedupon receptor.

1, which is tuned by condenser 2 to a chosen frequency. These signalsare then impressed upon the triode 3 and amplified thereby. Theseries-resonant circuit consisting of coil 14 and condenser 15 is tunedto another frequency and, therefore, does not by-pass a perceptibleamount of the desired incoming signal-energy from the amplifier 3. Theoutput from the amplifier 3 is then heterodyned, amplified and detectedin the usual manner.

In the presence of a powerful nearby station, the operator of thereceiving apparatus may have occasion to attempt to receive signals at afrequency which requires the local receiver oscillator to generateoscillation at a frequency which ,will simultaneously heterodyneoscillations of the frequency of the nearby transmitting station to thesame beat frequency as the desired signals. Thus the near-by stationproduces a troublesome interference. Under these conditions, the seriesresonant circuit is tuned to the frequency of the nearby interferingstation, whereupon it by-passes the oscillations in receptor 1 of theundesired frequency from the local sending station and prevents most oftheir effect upon the triode 3.

Unless the nearby station is extremely close, or of tremendous power,the single bypass circuit Will serve to remove so nearly all of theinterfering energy'that only an immaterial amount is conveyedthrough theheterodyne system and amplifier to the receivers.

Under extreme conditions of interference, however, a single drain coilmay be insuiiicient and a second drain coil may be provided as shown inFig. 2, wherein an inductor 16 and a condenser 17 are connected acrossthe terminals of the grid-coil 5 of the beat-resolving detector 8. Theaddition of the inductor 16 and condenser 17 will remove the mosttroublesome interference.

If but a single station produces interference, the parallel resonantcircuit may be tuned to the frequency of that station and may remaincontinuously adjusted to that frequency. If, however, a plurality ofstations are causing interference, the effect of all may be removed byinterconnecting condenser 15 and condenser 2 as shown in Fig. 2 in suchway that the frequency of the series resonant circuit is at all timessuch as to drain ofi" the frequency which is such as to he heterodynedto the same frequency as the desired signal. By employing thismechanical interconnection, there is but one so-called tuning hump inthe resonant system and the system as a whole is'responsive to but asingle frequency and is not responsive to other frequencies of whateveramplitude.

While I have shown but two embodiments of my invention in theaccompanying drawing, it is capable of various other changes andmodifications therefrom without departing from the spirit thereof, andit is desired, therefore, that onlysuch limitations shall be placedthereon as are imposed by the prior art or indicated in the appendedclaims.

I claim as my invention:

1. A signal-responsive system comprising an input circuit includingtuning means, an oscillator circuit, a filter circuit including tuningmeans, means for mechanically coupling said tuning means forsimultaneous adjustment to maintain the filter circuit so tuned as tofilter out an undesiredfrequency which differs from the frequency of theoscillator circuit by an amount equal to one half the difference betweensaid undesired frequency and the frequency of said input circuit.

2. A radio receiving system comprising means for tuning its input,adjustable means for reducing a desired signal frequency simultaneouslywith materially dilferent interfering signal frequency to the same lowerfrequency, variable means for removing the undesired frequency and meanscommon to said first named and said last named means for varying themslmultaneously.

In testimony whereof, l have hereunto suhscribed my name this 14th dayof February 1925. k

" GEORGE L. BEERS.

